Projection-machine illumination.



P. L. CLARK.

' PROJECTION MACHINE ILLUMINATION.

APPLICATION FILED SEPT. 6,1916.

Patented Dec; 4,1917.

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P. L. CLARK.

PROJECTION MACHlNE ILLUMINATION. APPLICATION FILED SEPT. 6. H316.

Patented Dec. 4, 1917.

3 SHEETS-SHEET 2.

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FIG.34

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FIG- 35 P. L. CLARK. PROJECTION MACHINE ILLUMINATION.

APPLICATION FILED SEPT. s. 1916.

1,248,456. I Patented Dec; 4, 1917.

3 SHEETS-SHEET 3.

x a Y JITI ' INVENTOR unrrnn STATES PATENT Orron.

rAUII L. CLARK, 0F BROOKLYN, NEW YORK.

Specification of Letters Iatent.

Patented Dec. 4, 1917 Application filed September 6, 1916. Serial No. 118,718.

To all whom it ma concern:

Be it known t at I, PAUL L. CLARK, a

citizen of the United States, residing at Brooklyn, in the county of Kings and State of New York, have invented a new and useful System for Projection-Machine Illumination, of which the following is a specification.

' .This invention relates to apparatus for illuminating a given area or areas, and more particularly to means for efliciently reflectmg and concentrating light rays emanating om one or more illuminants, upon a certain area of an opa ue picture or a transparent picture or slide or film as used in projection machines.

One object of the present invention is to provide means comprising a plurality of mirrors each of which reflects rays. of light received by it from a luminous source in such a manner-that a large proportion of the available light is transmitted to the desirably illuminated area. Another object is to provide means to illuminate a spot of givenoutline, said outline conforming approximately to the shape of the @picture to be projected. Another "object is to obtain .a spot of light at the picture plane of substantially uniform brilliancy and color over the greater portion of its surface. Still another object is to provide reflecting means of such construction that variations in color and intensity of the light at different parts of the spot are not increased by (a) inaccurate setting or alining OffihG carbons (b) the wanderin of the arc; (a) irregularities. in the reflectlng or refracting structure of the mirrors; (d) opaque parts of the lamp or mechanism intercepting some of the light; or, (e) by the uneven distribution of the light at difl'erent angles, which is characteristic of all commercial illuminants. Other objects-an advantages of the inven- .tion will be disclosed in the following specification, in the claims, and in the attached drawings, in which light source an 5 plurality of concave mirrors arranged in a Figure 1 is a (perspective view showing a a reflector comprising a rectangularbank in such manner as to refleet four beams of lightlto register upon substantially the same rectangular area.

This arrangement is somewhat similar to .that shown in Fig. 7 of applicantsiPatent No. 842,860, except that in the present devic'elthc'idea is to direct a plurality of beams upon the area to be illuminated, in-

- stead of a single beam, which Fig. 7 0f the above patent shows. Fig. 2 is a 'perspective view of a plurality of concave mirrors (which may be ellipsoidal, spherical, parabolic, or of other curvatures approximating the' above, or of combinations of two or more of them, or of the type called mangin mirrors, such as used in searchlamps) receiving light from the source shown and reflecting the light in a converging manner upon the area to be illuminated. Fig. 3

shows the cross-sectional appearance of a produced at the plane of the slide or 1m by the reflector shown in Fig. 2. Fig. 7 is similar'to Fig. 6, and shows the effect obtainable by adjusting the sections of the reflector, that is, by changing their angles or curvatures; or by varying the relative positions of the reflectors with respect to the illuminant. Fig. 8 is a front elevation, and Fig. 9 is a sectional view of Fig. '8 on B--B, showing a deep reflector. Figs. 10 and 11 area sectional view and a front elevation of a reflector comprising two sections of different curvature. Figs. 12, 13'and 14 are respectively a rear elevation; a sectional view on P-P, Fig. 12; and a front elevation of a four-part reflector having independently radjustable sections. Fig. 15 is an enlarged detail of the method of attaching a glass reflector similar to that shown. in Figs. 12,

13 and 14. Figs. 16 and17 are an end and. a front elevation of a concave reflector having vertical ribs for diffusing the light side-,-

wise. Fig. 18 is a section of Fig. 17 on (P C. Fig. 19 is a detail of a portion of the surface of a concave reflector provided with plane facets orslightly curved reflectingelements for giving variable horizontal and vertical dispersion from the reflector,

as a whole. Fig. 20 is a front view of a four-part reflector, whose adjacentvsections are provided with ribs at right angles to each other. Fig. 21 shows the cross-sec mounted for adjustment. Fig. 24 is a sec-' tion on DD, Fig. 23. Fig. 25 is a view showing the shape of the spot obtainable.

by using two complete reflectors of the type shown in Fig. 20. A spot of the shape here shown approximates that required to illuminate the border of a screen. Fig. 26 is a plan section on GG, Fig. 29, and shows a projector provided with an adjustable four-part reflector, a slide or film carrier or holder, an arc lamp, and a one-part objective lens. Fig. 27 is a section of Fig. 29 on E--E. Fig. 28 is an end elevation of Fig. 26 on FF. Fig, 29-isan end elevation of Fig. 26 on HH. Fig. 30 shows a quadrant of a round objective lens, drilled at the corners for the insertion of adjusting screws or guides. Fig. 31 is a side elevation of an incandescent lamp having a part of its glass bulb shaped and silvered to reflect the light in a plurality of converging beams. Fig. 32 is a view of Fig. 31 on KK. Fig. 33 is a sectional view of a concentrated filament incandescent lamp having the filament focused with respect to a number of reflecting sections at the rear of said filament, and having also a spherical reflecting front part, which utilizes certain of the light rays. Fig. 34 is a section of Fig. 35 on Ir-L. Fig. 35 is a front elevation of a concave reflector comprising eight independent units. Fig. 36 is a sectional view of a reflecting and refracting system comprising several adjustable members, and adapted to utilize substantially all the light from any suitable illuminant by directing nearly all the rays upon the area to be illuminated or projected for observation. Fig. 37 is a front elevation of the modification shown in Fig. 36. Fig. 38 is a sectional view of a reflector having concentric, spherical reflecting surfaces. Fig. 39 is a perspective View of a one-piece reflector having a plurality of contacting, concave sections. Fig. 40 is a front elevation of a quadrant of an objective lens, and shows the part of the lens that may be used in making a round unit. Fig. 41 is a front view of an achromatic lens combination, quartered and mounted in an adjustable case or lens tube. Fig. 42 is a section of Fig. 41 on M--M. Fig. 43 is a front elevation of a system having several complete reflectors like those in Figs. 12, 13 and 14. Fig. 44 is a sectional view of Fig. 43 on NN. Fig. 45 shows the overlapping of several spots to uniformly illuminate a given area. Fig. 46 is a sectional view showing the combination of an ellipsoidal and a spherical reflector. Fig. 47 is a section'of Fig, 43 on KR, and Fig. 48 is. 8.

section of Fi 47 on Q-Q, showing a modified form 0 the invention adapted to be rotated. Fig. 49 is a sectional view of a modified form of the device adapted for quick adjustment for a plurality of different size spots.

In the drawings the same parts appearing in the difierent views are similarly designated.

In Fig. 1 a plurality of concave mirrors 1, 1*, 1 and 1 are grouped adjacently so as to form a large surface exposed to rays of light from the illuminant 2. The curvatures and positions of the mirrors are such that rays from the said illuminant 2, when properly focused, will be reflected as shown by the arrowed lines. The rays received upon the bank of mirrors are those emanating from the illuminant 2 in an obtuse angle pyramid of substantially rectangular cross-section, which pyramid is radially divided by said mirrors into a plurality of acute angle pyramids of substantially rectangular crosssection and having Vertical sides. The bases of the several pyramids are seen to be juxtaposed, and the plurality of juxtaposed mirrors reflecting them have conjunctive poly onal peripheries; the mirrors are also shown as substantially contacting in planes radial to the axis of the reflector as a whole. front projection (or front elevation) of each mirror is substantially rectangular and of greater area than that of the device to be illuminated, and the several mirrorsconsidered as being of ellipsoidal or other mathe- 'matical configurationare arranged eccentrically (and not concentrically) with respect to each other, so that the interior angle between adjacent mirrors at any common point of juxtaposition is "less than 180 degrees. It will be noted that the rays from the mirror 1 do not cross (although they may be crossed either by using a mirror of shorter focal length, or by movin the light source farther from the reflectors but converge slightly to the plane 3, and the several converging pyramids of rays from the mirrors intersect each other at this plane, so that the area of maximum superimposition, thereupon, coincides substantially with that The of the spot illuminated by any single mirror.

It is evident that the size of the spot pro duced by any given'pyramid of rays is substantially in direct proportion to the distance of the plane of the spot from the apex of the pyramid. The shape of the spot of light from any single mirror as received upon the plane 3 is substantially rectangular, but the intensity of the light upon said spot will not necessarily be uniform throughout the same, on account of the variable distribution of light from the are or other illuminant, and for other reasons familiar to all. The intensitv of the rays reflected from the lower, left-hand corner means which produce a round spot.

of the mirror 1 will be greater than that of the rays from its upper right-hand corner, so that the spot on the plane 3 (provided this mirror alone is in service) will be brightest on its lower, left-hand corner. The

7 spot from the mirror 1' will be brightest at tion of slides and films, since these are generally square or rectangular; and by using the reflector here shown substantially all the available light can be concentrated to embrace the entire picture and need not greatly overlap its edges, as is the case where condensing lenses are employed, and otiier nother disadvantage of the round spot lies in its non-uniformity and in the presence 'of a fringed band or ring of yellow and blue which means considerable loss of form to the projected picture on thescreen. Even under the most favorable conditions it is noticeable that when using condensing lenses the corners of the pictures are not as well lighted as. the center. The form of the-invention shown in Fig. 1 produces a spot of light which is very white, shar and uniform throughout, and generally ree from color, except for a blue fringe at the edges. For best results I prefer that the reflectors 1, 1, 1 and 1 be of such curvature that the axes X of the pyramidal beams reflected from them intersect at or near the center of the plane 3, as shown, and at a substantially predetermined distance from the apexes of the several beams. Since the plane 3 intersects the several pyramids of rays between their bases and apexes the shape of the spot produced by each pyramid is similar to that of the front "projection of the mirror reflecting it, and consequently may be considered as an erect image (more or less out-of-focus, depending upon the dimensions of the illuminant and the distance of the plane of the spot from the base of the'pyramid) of the front projection of the mirror. The closer the picture is to the reflector section the closer will the outline of the spot, such as shown in Figs. 1, 2, 3 and 4, conform to the outline of the front projection of the mirror; if the picture is placed at the apex of the pyramid (the conjugate focus of the mirror) the spot will, of course, be in the form of a sharply focused image of the light source.

In Fig. 2 the reflector 135 is composed of a plurality of concave mirrors 4 which recelve rays from the source 5 and reflect them duce.

into a beam 8, which produces a spot 7, the

, general area and the result attained is the securing of a composite spot similar to those shown in Figs. 6 and'7.

In Fig. 3, the shaded area '9 around the white area IO-indicates the fringed portion of uneven brilliancy and color which appears at the plane 6, Fig. 2, when light sources of appreciable size are used, the width of the fringed area 9 being proportional to the dimensions of the source and the distance of the source and the reflector from the plane 6. When a glassreflector is used the Width of the fringe, as regards color, depends largely upon the refractive properties of the glass.

In Fig. 4 the shaded area 11 indicates the portion of the spot that would be produced by a point-source of light, provided part of the light is intercepted. The fringed area, resulting from the use of a source of appreciable dimensions, as noted in connection with the description of Fig. 3, is shown at 12, and the approximate portion of the light intercepted by the opa ue portion of the negative carbon and there ore lost, when a horizontal arc lamp is used, is shown by the shaded corner 13.

In Fig. 5 the mirrors 14 are. arranged as shown in order to twist through forty-five degrees the composite beam which they pro- It will be understood that certain cases will require the use of the modification here shown. The parts 14 are preferably of equal size, and are made by cutting a concave mirror into quarters.

I In Fig. 6 the plurality ofbeams from the quadrants shown in Fig. 2 overlap each other to the extent shown. It is seen that a large portion of the area is covered by all four of the. spots 1, 1, 1 and 1 The area 15 will be brilliantly and uniformly illuminated throughout; and minor irregularities in the structure of the reflecting surfaces of the curved mirrors, or unevenness of illumination occasioned by the wandering of the are or imperfect setting of the carbons, while affecting the individual beams, will injure the uniformity of the composite beam to a comparatively small extent.

In Fig. 7 the relative positions of the spots are different from those in Fig. 6, and I although the outline of the composite spot .is rectangular, it will be seen that the actual area 16 covered by all four spots is small and that it is tipped at an an le of fortyfive degrees to the vertical. he dimmest 7 portion of this spot gets light from two quadrants, however; whereas in Fig. 6 there are certain POSltlOIlS, at the corners, which 5 get light from only one quadrant. The

spots shown in Figs. 6 and 7 are symmetrical; but it should be understood that they may be of any desired form, either as shown or asymmetrical, and that the several beams can be brought into contact only, or overlapped or crossed to any desired extent and at any desired plane by tipping the reflectors properly.

In Figs. 8 and 9 the sections 17 are made deep in order to utilize a large proportion of the light from a properly placed source (not shown).

In Figs. 10 and 11 the mirror 18 is of such curvature and so focused with respect to the illuminant 20 that rays from 20 which strike it are reflected as shown by the arrowed lines 21, 22 and 23 to fall upon the plane 24 without crossing each other, and produce a semi-circular spot 25. The mirror 19 differs from 18 in curvature, so that whatever rays fall upon it are reflected to a focus at 26, thus producing an inverted and reversed image of the general shape of the front projection of the mirror 19 on the plane 24. The images or spots produced by 18 and 19 substantially coincide, as shown, and a dull spot on one side of either mirror caused by the wandering of the are or for any reason whatever, will be brightened and evened up by the beam of increased intensity received by the other mirror, and an even effect obtained.

In Figs. 12, 13 and 14 the mirrors 27 are symmetrically grouped about the optical axis A, and held in position on the frame 28 which carries three adjusting screws per mirror in order to make the reflector, as a whole, adjustable for different focal lengths. The corners of the mirrors are cut off at 29 to form a hole for the insertion of the illuminating device. The frame 28 is adj ustable on the standard 31 by manipulating the thumb-screw 30. By using a reflector of flint glass in combination with a crown glass objective lens, a partial achromatization is obtained.

In Fig. 15 the reflector glass 27 is drilled and two bushings 32, preferably resilient and of the nature of asbestos cloth, are inserted to separate the metal bolt 33 from the glass. Adjustment of the angle of the mirror 27 is made by turning the nuts 34, thereby causing a relative movement between the rigid frame 28 and the said mirror.

In Figs. 16, 17 and 18 the general curvature of the mirror 36 is the same as that of the mirror 1,. in Fig. 1. The surface of the mirror 36 is divided into a plurality of flat or slightly concave or convex ribs 37, the width 38, or transverse curvature of which determines the extent of sidewise dispersion of the mirror 36. When made of polished metal the reflecting ribs 37 'will be on the face of the reflector; but when of glass the simplest method is to grind and polish them on the back, or convex, side. The arrangement here shown will be found useful in cases requirin an oval or nearly rectangular spot, as escribed in connection with Figs. 21 and 25.

In Fig. 19 the relative length and breadth of the slightly curved elements or plane facets 45 is such as to affect the dispersion both in the vertical and horizontal direction. The use of this modification enables the securing from a round illuminant of a spot which is nearly rectangular, and as all the spots from the several elements overlap each other or register upon substantially the same area of the slide or film-a very high degree of evenness of illumination is secured.

In Fig. 20 the reflector 40 is composed of four sections each of which is ribbed as in Fig. 16. The object in having the ribs in the adjacent sections 41, 44, 42 and 43 at right angles to each other, and in the diametrically opposite sections 41, 42, 43 and 44 parallel to each other, is to obtain an even spot in case of uneven light distribution about the optical axis of the system.

In Fig. 21 the rounded corners of the spot 46 depend upon the diameter of the round illuminant furnishing the light.

In Fig. 22 the six sections 48 making up the reflector 47 will produce a substantially triangular spot when an illuminant is properly positioned with respect to each section and each of the said sections is inclined at such an angle that all of the spots register upon the same area.

In Figs. 23 and 24 a double convex objective lens has been quartered and the sections 50 are supported adjustably in the frame 51, so that each can be adjusted independently' by turnin the screws 53 bearing against the edges 0 the "sections; and the inside corners of all the sections can be adjust-ed longitudinally by means of the screw and nuts 52. In the use of reflectors of the several types hereinbefore described, it is advantageous that an objective of large diameter be employed, since the several spots 49 are received at the plane of the objective some distance from the center of the lens. On account of the edges of the lenses being used the images produced by these several separated spots are apt not to coincide upon the screen, although the image resulting from the bundle of rays in each single spot is in itself well defined. In order to bring the several images into coincidence at the focal plane of the screen it is necessary only to adjust the screws 52, 53. By using the arrangement here shown ordinary spherical objectives of large diameter can be used, and' the disadvantages of chromatic and spherical aberration partly obviated by tipping each section 50 at the proper inclination to the incident beam. The arrangement here disclosed will be found advantageous for medium and short focal length systems.

A the arc lam 62 are concentrated by the adjustable re ector 63 (similar to that shown 1n Figs. 12, 13 and 14) upon the film 64, as shown by the arrowed lines 61. These rays strike the objective lens 65 in as many spots as there are mirrors 67, namely, in four spots 62 (Fig. 28), and the beam pass ing through the lens at any one of these spots contains rays embracing a certain portion-either part or all-of the picture on the film to be projected. The shape of the composite spot at the picture plane will be substantially similar to that shown in Figs. 6 and 7, depending upon the position of the lamp and the curvature and arrangement of the mirrors, as before pointed out. In order to shield the film from direct exposure to the are a condensing lens or flat piece of glass 73 is mounted as shown, in the casing 70. A horizontal slot 74 is provided (Fig. 29), which permits sliding in sidewise the lamp and mechanism 71 on the base 68. A suitable casing 70, the reflector stand 72 and the objective lens holder 69 are suitably mounted upon the base 68. Since the portions of, the objective used are near its edge considerable chromatic aberration is noticed when the rays from only one spot are projected (the light from the other spots being cut off in the experiment, by an opaque shields; but'when all four beams are projected substantially all objectionable colored fringe disappears, and a sharp image is secured, since the colored fringes caused by the refraction of the light from the four quadrants of the lens 65 neutralize at the screen. The arrangement here shown (Figs. 26-29) contemplates focusing the system so that the four images of the illuminant will be produced at, or near, the objective lens, and symmetrical with respect to the optical axls of the projector. It will be understood, however,

that this invention would include the ideaof focusing so that the several images or distorted images of the illuminant be produced at the plane of the picture 64, or at any desired place either in front or back i of the said picture, or at any'combination of places. Figs. 10 and 11, before described, show the rays from one reflector brought to a focus 26 in front of the picture, and the rays from the other reflector focusing at a point back of the picture. The reflectors are preferably of such curvature and so positioned with respect to the illuminant that each would coincide substantially with an ellipsoid whose major axis passes through the illuminant and also through the reflected image of the said illuminant. As

the several reflected images areproduced at separated spots and the illuminant is in, a

fixed position, it is evident that the axes of or at a negative distance from focal plane of the illuminant.

In Fig. 30 the lens section 50 is rovided with holes or depressions 49 for t e'inse'rtion of screws 53, shown in Fig. 24.

In Figs. 31 and 32 substantlally one-half 77 of the glass bulb 76 is spherical and clear, while the other half is sllvered and made up of a number of curved arts 78 of suitable configuration and so ocated with respect to the illuminant 79 that rays from it will be reflected by them in a manner similar to that described in connection with Figs. 1 and 2, and will pass through the clear front to the desired area of the slide through to illuminate the space of desired size and shape. The surface 85 is spherical with respect to the filament 83 as a center, so that rays which strike this surface are reflected back to the intersecting ellipsoidal mirrors 82 and by them outwardly, as shown by the arrowed lines 88. The lamp should be blown of thin glass, and thebentsupport 89 which carries the filament, and the base 90 can be of any desired form.

In Figs. v34 and 35 the mirrors 91 are arran ed to provide an openin 92 for the insertlon of the desired illumlnating mechanism.

In Figs. 36 and 37 a plurality of ellipsoi- 94 are adjustably mounted on a suitable framework 95 which, in turn, is carried by the standard 98. .An illuminant 96 is held on the support 97 at the focus of the ellipsoidal, and the center of the spherical reflectors. A hemi-spherical reflector 99, having an opening 106, is mounted to slide u on horizontal Ides 100. A condensing ens 101 is held in position in front of the lamp dal reflectors 93, and a sphencal reflector 96 by means of the support 102 attached to the lamp holder 97, so that the rays from the lamp are concentrated upon the area whose center is at the point 103 in the focal plane 104. The diameter of the lens 101 and its mountin 107 is such that the angle subtended by 1t with respect to the lamp filament as the apex is substantially the same as the angle subtended by the opening 106 in the reflector 99, so that no direct rays of light from the lamp will pass through the said opening 106. The spherical mirror 94 is placed behind the mirrors 93 in order to increase its distance from the lamp so that the size of the spot which it would produce shall be kept down. Rays from the lamp striking the mirror 94 will be reflected back upon themselves and will pass through the condenser in the same manner as direct rays from the said lamp. The angles subtended by the mirror 94 and the lens 101 are substantially equal. The paths of the rays are shown by the arrowed lines 108. Rays from the lamp which strike the mirror 99 are reflected back upon themselves and fall upon the ellipsoidal mirrors 93 and are reflected by them directly through the opening 106 to the spot at the focal plane 104. The apparatus here shown produces nine separate spots at the plane of the objective lens (instead of the four spots, as in Fig. 28)'one spot for each mirror 93 and one for the combined condenser 107 and the mirror 94. On account of the spreading of the light, due to the size of the illuminant, the size of the composite beam near the plane 104 will be somewhat as indicated at 105. The several parts of the reflecting and refracting system are adjustably mounted on the base 109, and covered by a suitable casing 110. This form of the invention bottles up substantially all of the light and directs it with accuracy to the area to be lighted; and the spot produced by the nine beams can be made reasonably small and uniform throughout, or non-uniform or shaded to any desired extent by varying the angles of one or more mirrors 93, or by other adjustments within the scope of the apparatus. In case an arc lamp is used the opening 106 may be closed by a flat glass sheet. By sliding the reflector 99 forwardly on the rods 100 the lamp 96 can be removed readily. The mirrors 93, 94, for best results, should be designed to receive one-half or more of the light, in order to reduce the losses caused by double reflection, and to utilize the rays emanating from the lamp in a vertical plane.

In Fig. 38 a plurality of concentric refleeting zones 113, 114 and 115 of different radii 1' r 1', are connected by the conical portions 116 and 117. The advantage of this reflector lies in its small diameter, in comparison to the large radii of its reflecting zones and the smaller angle subtended by the opening 118 with respect to the center 119. This reflector can be substituted for the reflector 99, Fig. 36.

In Fig. 39 the reflector 120 is composed of fourellipsoidal parts 121 contacting at the lines 122. This modification can be made of glass or metal and provided either at the back or sides with one or more holes 123 for the insertion of an illuminant.

In Fig. 40, 125 indicates the outline of a quadrant of an objective lens. On account of the difliculty of mounting this shape in an air-tight manner in a lens tube, I prefer to cut out a round disk 126 from the center of the quadrant. The approximate position of the spot from one mirror in a four-part reflector (as shown in Fig. 28) is indicated at 127.

In Figs. 41 and 42 the lenses 127 are quadrants of a complete achromatic combination and are held in tubes 128 by flanges 129. Slotted lugs 130 are provided on each tube 128 and the tubes are adjustably held by the screws 131 in proper relationship within the flanged casing 132. The position of the intersections of the beams with the lenses is shown at 133. It is well known that the sharpest images are secured by utilizing a small portion only of the ordinary projector objective, and certain of the arrangements herein shown which contemplate using several separated spots near the periphery will produce at the screen a plurality of non-coincident images, and my object in varying the angles of the lenses with respect to the optical axis of the system is to bring the plurality of separated images into coincidence and focus.

In Figs. 43 and 44 a plurality of fourpart reflectors 135 (similar to those shown in Fig. 2) are adjustably mounted on a frame 136 and an illuminant 137 is placed at the focus of each reflector so that the light as a whole is directed to converge upon the desired surface. This combination will produce sixteen spots at the objective lens, and has the advantage of being adapted for a plurality of illuminants, so that a very brilliant image can be projected.

In Fig. 45 the spots 138 overlap each other, as shown. This arrangement will exist at the plane where the film or picture is positioned when eight round reflectors are used, provided all the beams substantially coincide at a single spot or be slightly separated at the objective lens. The intensity of the light reflected from the edges of a deep circular reflector is less than that from the inner portions; and by properly adjusting the overlap of the beams at the plane of the picture it is possible to get a fairly uniform field and at the same time to concentrate the beams upon a small area of the objective lens. The approximate shape of In Figs. 47 and 48 a plurality of reflectors 145 are held in position by the concave member 146 having the conical flange 147. A hollow spindle-148 is mounted in the bearing 149 and to this spindle is rigidly secured:

a driving pulley 150 and also the support 146 and a retaining ring 151 which keep the reflectors in position. Attached to and insulated from the bearing support 152 is the arm 153 which carries a tube 154 entering into the hole of the hollow spindle 148, and acting as a guide for the negative carbon holder 155. When the reflectors are not rotated the individual or composite spots produced by them will be similar to those shown in Figs. 3, 4, 6, 7 or 45; but when rapidly revolved the irregular spotdue to the persistance of vision.appears as a round disk of even light. The speed of the reflectors should preferably be such that a complete revolution or over is made for each exposure of the moving picture film. This modification .is advantageous even when revolved at a slow rate, inasmuch as the heating of the glass mirrors by the arc is equalized,

- and the breakage liability reduced.

In Fig. 49 a plurality of reflectors 160 are flexibly attached at their outside corners by studs or screws 161 to the rigid backing 162. The inside corners of the reflectors are flexibly held in an annular groove 163 at the end of a tube 164, through which freely passes the negative carbon and holder 165. The tube 164 slides in the support 166 and has a given lateral motion with respect thereto. A ring 167 having two suitably spaced annular grooves 168 is attached to the tube 164, and fitting into these grooves is the curved free end 169 of a flat spring 170 attached to the support 166. By pushing the tube 164 into the support the inside corners of the several reflectors are thrust forward (the reflectors assuming a position as shown by the dotted lines 160) and the composite spot of light is produced at a greater distance from the reflectors than when the tube is in the position shown by the drawings. This form of the invention will be found'useful in cases where a quick change is to be made from'a moving picture to a stereopticon slide. As a large spot is required for the commercial sizes of slides, it is necessary'that the slide be placed much closer to the reflectors thanthe moving picture film, on account of the small spotrequired for the latter; and the form of the device here shown permits a rapid change at will of the focal distance of the reflector system, a simple movement of the tube 164 producing a composite spot of substantially predetermined size (the illuminant being considered of a given size and at the focus of the system) at a given distance.

The several forms of the invention hereinbefore described will be found of value when used in connection with a screen whose surface is made up of specular elements, since the-glare in any direction caused by imperfect flattened portions of one or more of the elements will be reduced in direct proportion to the number or the size of the independent spots passing through the objective, as in Figs. 26, 27 and 28.

In the modifications employing several separate reflectors each reflector 1s, preferably, attached to the framework supporting it by adjusting screws, so that each member can be adjusted independently. The form shown in Fig. 49 is also adapted for adjustment as a whole. Certain features shown in some of the modifications can be applied to other modifications where desired, in order to secure flexibility of operation or for other purposes within the scope of this invention. What I claim is:

1. In combination with a projector having a source of light and a device to be projected upon a screen, means for concentrating light rays upon said device comprising a plurality I of concave mirrors each disposed to reflect a beam of rays derived from said source to converge upon and substantially embrace the said device; substantially as described.

2. In combination with a projector, a reflector comprising a plurality of juxtaposed concave sections each disposed to receive rays from a single source of light placed at one of its foci and reflect and converge them to produce a spot of light upon a plane at a distance from the said source less than the distance between the source and its conjugate focus, and means for bringing the spots into coincidence at will; substantially as described.

3. A reflector comprising a plurality of juxtaposed concave mirrors substantlally contactingin planes radial to the axis of the said'reflector, and arranged obliquely posed with relation to each other, substantially as described.

5. A reflector comprisin a plurality of mirrors of substantially e li soidal curvature eccentrically disposed wlth relation to each other, and means for varying their eccentricity at will; substantially as described.

6. In combination with a projector provided with a single source of li ht, a plurality of concave mirrors'each isposed to swing about an axisat right angles to the axis of the projector and reflect a converging beam of light derived from the said source to cross the said axis, and means for simultaneously and equally varying the angles of the mirrors with respect to the said axis, and means for retaining the said mirrors in a plurality of predetermined positions to cause the several reflected converging beams of light to intersect each other where their cross-sections are of substantially predetermined sizes; substantially as described.

7. In combination with a projector provided with a source of light, light deflecting means comprising a plurality of juxtaposed quadrants of a concentrating reflector disposed behind said source, oblique to each other and symmetrical with respect to the optical axis of the projector; substantially as described.

8. In combination with a projector provided'with a source of light and a device to be projected, light deflecting means comprising a plurality of juxtaposed sectors of a concentrating mirror disposed behind said source and receiving rays therefrom and reflecting them in the form of erect images of the front projection of each of the said sectors to embrace the said device; substantially as described.

9. In combination with a projector provided with a source of light and a picture to be illuminated for projection upon a screen, light deflecting means comprising a plurality of juxtaposed mirrors disposed to receive rays from the said source and reflect them to produce at the plane of the picture an out-of-focus image of each of said mirrors; substantially as described.

10. In combination with a projector provided with a source of light and a picture to be illuminated for projection upon a screen, light deflecting means comprising a plurality of juxtaposed mirrors disposed to receive rays from the said source, and reflect them to form an image of each of said mirrors at the plane of and embracing the said picture; substantially as described.

11. In a projector, in combination with a source of light, a plurality of concave mirrors arranged oblique to each other and with one conjugate focal point of each mirror substantially coincidin with the said source of light; substantial y as described.

12. In a projector, in combination with a source of light and a picture to be projected positioned on the optical axis of the said projector, a plurality of concave reflectors disposed to concentrate light from said source upon said picture, one conjugate focal point of each of said reflectors coinciding substantially with the said source and the other conjugate focal point of each reflector lying off the said optical axis; substantially as described.

13. A reflector comprising a plurality of identical ellipsoidal mirrors having conjunctive polygonal peripheries, one focal point of all the mirrors being coincident and the focal points conjugate being non-coincident; substantially as described.

14. In a projector, in combination with a source of light and a picture to be projected positioned on the optical axis of the said projector, a plurality of concave mirrors disposed to concentrate light from said source upon said picture, and means for maintaining one focal point of each mirror at the said source and its conjugate focal point a given distance from the said optical axis; substantially as described.

15. In a projector, in combination with a source of light positioned on its optical axis and a picture to be projected, a plurality of reflectors disposed to concentrate beams of light derived from said source upon said picture, the center of the picture lying on the optical axis of the projector and also on the axis of each of the reflected beams and in a plane between the conjugate foci of each mirror and normal to the said optical axis; substantially as described.

16. In combination with a projector provided with a source of light and a picture for projection, light deflecting means for directing a plurality of convergent beams of light derived from said source to intersect each other at substantially the plane of said picture, the said plane lying between the focal plane of the said source and the source itself; substantially as described.

17 In a projector, in combination with a source of light and a picture to be projected, a plurality of mirrors for reflecting a plurality of beams of light derived from said source to intersect each other at substantially the plane of the said picture, the crosssection of each of said beams where it intersects the said picture being of a shape substantially the same as that of the front proj ected area of the mirror reflecting it and of a size substantially embracing the said picture; substantially as described.

18..In combination with a projector having a source of light, a device to be projected upon a screen and an objective lens, light deflecting means disposed to receive a pyramid of rays emanating in an obtuse solid angle from the said source and radially divide said pyramid into a plurality of acute-angle pyramids having substantially juxtaposed bases, and deflect the said pyramids so that their axes substantially intersect each other on the optical axis of the projector and at a predetermined distance from their apexes; substantially as described.

19. In combination with a projector having a source of light, a device to be projected upon ascreen and an objective lens, light deflecting means disposed to receive a pyramid of rays emanating in an obtuse solid angle from the said source and radially divide said pyramid into a plurality of acute-angle pyramids having substantially,

juxtaposed bases, and deflect the said pyramids so that their axes substantially intersect the said objective lens at a plurality of points equidistant from the optical axis of the projector substantially as described.

20. In combination with a projector having a source of light and a device to be projected upon a screen, a plurality of light deflectors disposed to receive -a pyramid of rays emanating in an obtuse solid angle from sald source an radially divide said pyramid into a plurality of acute-angle pyramids and deflectmore than one of said pyramids to embrace substantiall the entire surface of the device to be pro ected; substantially as described.

21. In combination with a projector having a source of light and adevice to be projected upon a screen, light deflecting means dlsposed to receive a pyramid of rays emanating in an obtuse, solid angle from said source and radially divide said pyramid into a plurality of acute-an le pyramids the cross-section of-each of w ich, normal to its axis, is substantially a rectangle having vertical sides and deflect said yramids so that their axes intersect each ot er at the center of the said device; substantially as described.

22. In a projection machine provided with an illuminant and a device to be projected for observation, the method of obtaining a uniform spot of light u on the said device which consists in supenmposin thereon a plurality of beams of light sac of which is of non-uniform composition and contains the rays emanatin from the said illuminant in one of a pluraht of substantially juxtaposed fyramids; su stantially as described.

23 n a projection machine provided with an illuminant and a device to be projected for observation, the method of obtaining a substantially rectangular spot of light at the said device which consists in superimposing thereon a plurality of beams of light each of which contains the rays emanating from the illuminant in one of a plurality of substantially juxtaposed pyramids of rectangular cross-section; substantially as described.

24. In combination with a device to be illuminated and a single source of light having a non-uniform distribution, light defleeting means receiving rays from said source and directing them in the form of a plurality of converging beams of non-uniform composition upon the said device so that areas of high intensity in one or more beams are superimposed upon, areas of less intensity in other beams; substantially as described.

25. In a projector having a device to be illuminated by directing upon it a plurality of beams of non-uniform composition, the method of obtaining an even illumination upon the said device which consists in superimposing certain areas of substantially mean intensity of each of the said plurality of beams upona given area of the said device and superimposing upon each adja cent area thereon rays occupying other areas of the several beams, so that the sum of the intensities in these said other areas approximates the sum of the intensities in the aforesaid areas of mean intensity; substantially as described. u

26. In combination with a device to be illuminated and a single source of li ht having a non-uniform distribution, light deflecting means receiving rays from said source and directing them in the form of a plurality of substantially identical conver ing beams of gradually variable intensity in different zones, so that zones of given intensity in one of the beams are superimposed upon zones of a different intensity in the opposite beams at the plane of the said device; substantially as described.

27. In a projector having a device to be illuminated by means of a plurality of separate beams of light, themethod of illuminating the said device which consists in superimposing the several beams upon each other and upon the said device so that the outline of the area of maximum super-impo- 

